Slurry polymerization process



Nov. 10, 1953 w. G. MAY ET AL 2,658,933

` SLURRY POLYMERIZATION PROCESS Filed Aug. 1'7. 1951 2 Sheets-Sheet l O9 4.5 QEAToQ ElFfFLuskw-r hJlter @.maj Graven-tors orge 1..,mathesor125%,; )n ttornev NOV. l0, 1953 W G, MAY ET AL 2,658,933

SLURRY POLYMERIZATION PROCESS Filed Aug. 17, 1951 2 sheets-sheet 2TIQf'Z w/c'lter 6.mo ovedters George Lmotheson.

Patented Nov. 10, 195.3

UNITED STATES PATENT olf-Fics 2,658,93'3 Y Y .Y ,Y SLURRY POLYMERIZATIONPROCESS Walt-er G.V May, Roselle, and George Matheson,

Summit, Nr.1., assignors to Standard Oil Development Company, acb'rporati'on of Delaware Apg-)licence August 17, 1951, serial No.242,208

, ,This invention is concerned with the-polymerization of low molecularweight olens to -v produce low molecular weight polymers boiling in thegasoline boiling range employing a.Y 'finely- -divided, solid phosphoricacid catalyst maintained as an agitated suspension or slurry in a fluidhydrocarbon phase. Theinvention is particularly concerned with a methodof recovering and revivifying agglomerated catalyst that forms duringthe polymerization process.

It is known to polymerize normally gaseous olens such as olens bycontacting them with an agitated slurry or suspension of finelydivided,solid phosphoric acid catalyst in a highly dense, fluid hydrocarbonphase. The process has -a number of advantages over conventional 'Xedbedor low pressure Ifluidized catalyst cperations from standpoints such vasheat control main- `tenance, improved polymer yield, catalystreplacement and the like However, one disadvantage encountered in the`slurry-type operatien lis that certain solid phosphoric acid catalyststend to agglomeratie into lumps or cake aftereitended operation periods.Apparently the catalyst adsorbs high molecular weight bodies ofdifferent types which causethe particles to cohere'. The coheringparticles are difcult to maintain suspension and' aresub'- stantiallyinactivea There are at least two diffferent types of catalystagglomerates. type comprises lightrclored balls,A putty-like appearance,havingA particle sizes up to about 2 inches in diameter. Anotherdistinct type comprises dark-colored agglomerates 'of individualparticles coated with carbonacecus materials. The agglomerates, inaddition toA being' substantially inactive with respect topolymerizationi activity, cause mechanical difficulties such as breakingthe blades of mechanical agitators em#- ployed to maintain the catalystsuspension and the like.

It has been proposed to prevent catalyst agglomeration by cosuspen`din'gwith the catalyst a finely divided, solid adsorbent which has sub#stantially the same settling characteristics as the catalyst and whichis substantially inactive in the polymerization step. Such soliddiluents 1include silica gel, activated carbon, alumina and the like.The use of such adsorbents leads to decreased utilization of reactoryspace and, in some cases, the diluent adsorbs phosphoric acid from thecatalyst and `gradually deactivates it.

It has been proposed in patent application Serial No. 208,507,1iled June30,l 1951,- in the name vof ,Sumner VB. stveetser, that a'.g'gloniera,i

The iirst 11 claims. (c1. .260;68315) 2 tion be preventedmby washing thecatalyst continuously orA intermittently -with an aromatic solvent orthe like, ,A to remove high molecular weight materials from the catalystbefore it agglomerates. This procedure is disadvantageous from thestandpoint that much of Athe catalyst vwhich is still active must bewashed with a` solvent. On theother hand, it is notfeasiblel to includean aromatic solvent or the like along with the reactants inthe reactionzone to prevent agglomeration since such materials enter into thereaction andproduce undesirable side products.

It is the object of thepresent invention to disclose a means forremoving catalyst which is agglomerated from the reaction vzone,`washingonly the agglomerated catalyst with a suitable solvent whereby thecatalyst is deglomerated and reactivated, and returning the activatedcatalyst to the reaction zone., The term de'glomerated as used herein.refersto separation or breaking down of the agglomerated mass intoparticles ofsub- -stantially the same size as the catalyst particlesthat cohered.

The polymerization reaction is conducted in such manner thatunagglomerated catalyst is Amaintained in slurry form by suitableagitation or fluidization means. As the catalyst agglomerates, it issettled or otherwise removed from the main body of slurried catalyst andis subjected to Aa treating operation as hereinafter described. Thisprocedure provides a means of treating only a limited portion of thecatalyst and permits maintenance of catalyst activity at a relativelyhigh level by a rather simple expedient.

The slurry polymerization of normally gaseous olens is usually carriedout in a single zone, or in multiple zones in series or paralleloperation, which aremaintained' at temperatures in the range of about350 to 600911". and at pressures abovey about 45011. s; i. g.v Thecatalyst is-maintained as a `dense yslurry in a fluid hydrocarbcn phasecomprising olens, paraflinic diluents and polymer. It is agitated bymechanical agitation,

or by nowing olefin feedzand/or recycled reactor eluent up throughl thecatalyst mass,zor by other substantially equivalent means. The reactionzone maybe of vthe .hindered settler type wherein adense catalyst phaseexists in the lower portion thereof, and ai hydrocarbon phase islsuperimposed above it rom which a reactor eluent'substantially freer OfCatalyst is Withdrawn.

'rhs-'fluid hydrocarbon' phase in whichth'e cataiy'st is suspendedishi'gh'ly dense and mayfb' a4 liquid phasga'highly d''nse vaporphaseatfhigh pressures, or acritical phase at' pressures above several,procedures.

merization operations, feed and/or recycled euin Whole or in part to theliquid phase for fluidization purposes.

The solid phosphoric acid catalyst used in the practice of the presentinvention usually comprises about 50 to 90 weight per cent phosphoricacid, based on the total weight of the catalyst, deposited on orimpregnated in a solid adsorbent carrier. The invention particularlyapplies to solid phosphoric acid catalysts which tend to agglomeratiewhen suspended in a dense hydrocarbony phase under polymerization Yconditions of temperature and pressure. In particular it has been foundthat catalysts having siliceous bases,

The agglomsuch as propylene. The finely divided catalysts of the presentinvention refer to those having particle sizes in the range or about 2oto 200 mesh r smaller. Y

The agglomerated catalyst may be removed from the main body of thecatalyst by one of In hindered' settler polyent are charged upwardlythrough the catalyst mass to keep it in suspension. It is preferred thatthe fluidization velocity through the catalyst be somewhat abovethefluidization velocity required to keep the largest unagglomeratedcatalyst particles in suspension, but below the fluidization VvelocityVrequired to suspend the smallest agglomerated catalyst masses whichform. This permits maintaining the unagglomerated catalyst insuspension, and agitating the contents of theY zone whereby good mixingis achieved such that the olens are thoroughly contacted with thecatalyst. As the catalyst agglomerates, however, it will reach a size atAwhich its minimuml fluidization velocity exceeds the fluidizingvelocity actually used in the zone. It will then settle to the bottom ofthe zone .for removal therefrom in accordance with the practice of thepresent invention.

In mechanically-stirred reaction zones, where the suspension of catalystis independent of iiuidization velocities, catalyst agglomeratesof suchsize will form that will eventually settle to the bottom of the reactor,agitation by mechanical means being insuicient to maintain them insuspension. The agglomerates may then be removed and treated. Since theagglomerates sometimes cake on the blades of mechanical stirringdevices, orcause other mechanical diiculties, it is generallypreferredfto pass continuously the dense catalyst slurry from themechanically agitated zone to a hindered settling zone, wherein sub`stantially all of the agglomeration occurs and in which the agglomeratedcatalyst is settled from 4 ing the catalyst particles together. Solventsthat comprise relatively low boiling aromatic hydrocarbons are generallypreferred; however, other compounds having equivalent solvent propertiesor fractions rich in low molecular weight aromatic constituents may beemployed. In general, aromatic solvents are selected from those having asingle aromatic ring.Y It is preferred that alkyl aromatic solvents suchas, for example, xylene be used. It is also preferred that the alkylgroup have no more than two carbon atoms in the chain. y While thepreferred solvent comprises xylene, other aromatic solvents such asbenzene, toluene, ethyl benzene, mesitylene or the like, or theirmixtures may be employed.

The invention will be illustrated in connection with the accompanyingfigures in which:

Figure 1 illustrates a hindered settler polymerization zone and washingzone; and

Figure 2 illustrates an operation in which the catalyst is removed froma mechanically agitated zone into a settling zone, from whichagglomerated particles are removed and washed in a mul- .ing in thegasoline boiling range.

tiple batch system.

4Referring .to Figure 1, the numeral Il designates a hindered settlerreaction zone in which a finely divided catalyst, such as phosphoricacid deposited on silica gel and having a particle size in the range ofabout 60-100 mesh, is suspended in a single hydrocarbon phase at apressure of about 1000 p. s.I i. g. An olen feed comprising about 50%Cs-Cr olefins is introduced into the lower portion of zone il by meansof line I2 and passes upwardly .through the hydrocarbon phase at afiuidizing velocity such as in the range of 2 to 6 feet/minute suicientto keep the agitated catalyst particles in suspension in the lowerportion I3 of zone l l. A clearly defined interface exists between thecatalyst slurry suspended in the upowing hydrocarbon stream, zone i3,and the clear hydrocarbon zone above containing no catalyst, zone I4,Substantially catalyst-free eiliuent comprisingpolymer is withdrawnthrough line l5. Zone H is maintained at a temperature of about 459 F.,under which conditions sub- Ystantialrproportions such as '75 to 90% ofthe oleiins are converted to dimers and trimers boil- If desired, aportion of the reactor eiiiuent may be recycled through line i6containing valve 9 and pump l0 to the lower por-tion of zone Ii in orderto hel will gradually become .coated with high molecular weight polymersor carbonaceous materials, and the particles will cohere .into.agglomerates Yhaving a iiuidization velocity greater than thatmaintained in the reaction zone. The agglomerates will settle into thelowerconical portion I1 of zone Il. Fromtime to time the agglomeratesmaybe withdrawn from zone I1 into accumulation zone i8 by proper controloflvalve'l, and the agglomerates Vmay then be transferred through line2t having valve'2l into the top of treating tower 22. A stream ofaromatic solvent such as, for example, xylene, is introduced at thebottom of treatingtower 22 vby means of line 23. The settlingagglomerated catalystis coun'- tercurrently washed by the stream ofxylene flowing upwardlyV through the tower. A hydrocarbon mixturecomprising xylene, the small amount of hydrocarbons in which thecatalyst was suspended, and the materials dissolved'from the catalystis` withdrawn from Ythe topof tower 22 v through line'24.; Thismixture'is sent to a recovery system, not shown, for separation ofxylene from contaminating materials by distillation or other means, andthe substantially purified xylene is recycled to tower 22 by means ofline 23.

The catalyst agglomerates which pass downwardly through tower 22 incontact with the solvent are gradually broken up into revivied particleshaving substantially the original size of the catalyst in the reactionzone by dissolving adsorbed materials therefrom. The catalyst particlessettling to the bottom of tower 22 may then be Washed with a parafnicsolvent, such as hexane, which is introduced by means of line 25. Thusthe catalyst which is substantially free of polymerized or other highmolecular weight bodies is also washed substantially free of xylenebefore being recycled to the reaction zone.

A slurry of the catalyst is then withdrawn from the bottom of tower 22by means of line 216 and is preferably mixed with at least a portion ofthe fresh olen feed passing through line 21. The suspension is passedthrough line 21 containing pump 21a, to line i 2 and thence to thereaction zone. In this manner the reviviied and deglomerated catalyst iscontinuously or intermittently introduced into the main body of thesuspended catalyst in zone I i.

Referring to Figure 2, catalyst is maintained as a dense suspension influid hydrocarbon comprising olefin feed in zone 30. The contents arethoroughly agitated by means of stirrer 3| actuated by prime mover 32through shaft 33. The slurry of catalyst and hydrocarbon is continuouslywithdrawn from zone 30 through line 34 and is passed into the upperportion of hindered settling zone 35. A dense catalyst slurry ismaintained in the lower portion of zone 35 and a clear hydrocarbonphase, containing substantially no catalyst in the upper portion, zone35. Effluent is withdrawn from phase 3&3 through line 31, and a portionof the effluent is recycled through branch line 38 into the lowerportion of the dense catalyst phase in zone 35. Olencontaining feed isintroduced into the lower portion of zone 3o through line 39. A portionof the dense catalyst phase may be continuously passed from zone 35through line it and line 39 into zone 30. If desired, a portion of thecatalyst slurry may be withdrawn from the system through line lil andreplaced by fresh active catalyst introduced into zone 30 through line29 as a slurry in a hydrocarbon or the like.

Reaction conditions are conducted such that a portion of the olenpolymerization occurs in zone 30. However, substantial polymerization aswell as most of the catalyst agglomeration occurs in zone 35. Catalystagglomerates settle into the lower conical portion 42 of zone 35, andmay be removed from the system into accumulation zone 43 through valve44.

Agglomerated catalyst is then passed through line 45 by controllingvalve :i6 and is charged into initial treating zone 41. A primarysolvent, such as xylene, is fed into the bottom of the initial orprimary treating zone 41 by means of line 4S and is withdrawn from thetop of this zone through line 69. A stirrer 50 is provided to maintainintimate contact between the agglomerated catalyst and Xylene. A slurrycontaining partially deglomerated catalyst is withdrawn by means of linel and is introduced into a secondary treating zone 52 containing stirrer53.

Xylene is introduced into zone 52 through line 54 and is withdrawn bymeans of line 5 5. The

catalyst is further Washed and contacted with the Xylene in this zoneand is then withdrawn through line 56 and introduced into atertiary zone51. This zone is agitated by stirrer 58, and a secondary solvent such asnormal hexane is introduced therein by means of line 59. In thismodification, a portion of olen feed may be passed from line 39 throughline It) with or without the hexane solvent to wash the catalystcompletely free of xylene. The aromatic and non-aromatic solvents arewithdrawn from zone 51 through line 6l and are sent to a suitablerecovery system, not shown. Deglomerated catalyst, washed substantiallyfree of high molecular weight bodies and aromatic solvent, passesthrough line 62 and is mixed with olefin feed in line Sil, through whichit passes to zone 30. Suitable control valves may be provided in all thelines where they are not shown explicitly.

While two systems have been described for removing and treatingagglomerated catalyst particles, it Will be obvious to persons skilledin the art that other equivalent separation and treating procedures maybe used to accomplish the objects of the present invention. The solventWashing of the agglomerated catalyst may be carried out by usingintermittent batch treatment in a single treating zone. In connectionwith Figure 2, for example, treater 41 may be partly filled with theagglomerated catalyst and the treater then filled with aromatic solvent.After sufficient agitation such as, for example, several minutes. thebull: of the Xylene may be withdrawn, leaving a slurry of partlydeglomerated catalyst therein. A second charge of fresh xylene may thenbe added to the zone foi` further washing and deglomera tion of thecatalyst. This process may be repeated as many times as necessary todeglomer ate and revivify the catalyst. The catalyst may then be given afinal washing with a non-aromatic primary solvent such as a paraffnic orolenic stream to remove aromatic material before the catalyst isreturned to the reaction zone for further use.

The agglomeration of catalyst will be relatively slow and frequentlywill not occur in appreciable amounts until after the reaction hasproceeded from 50 to 100 hours or so; therefore, the capacity of thetreating system will be relatively small in comparison to the reactionand/or settling zone capacities. The treating operation may be conductedat a pressure and temperature substantially the same as that employed inthe reaction zone. Frequently, it will be desired to carry out thewashing step at about '15 to 125 F. below the polymerizationtemperature. A preferred treating temperature is in the range of about300 to 350 F. In separating agglomerated catalyst from unagglomeratedcatalyst in a hmdered settler-type zone, it will generally be necessaryto maintain luidization velocities up through the zone in the range ofabout l to l0 feet per minute at the pressures used in the reactionzone. Preferably, the fluidization velocities will be above about 0.6feet per minute, partlcularly when the pressures are maintained abovethe critical for the hydrocarbon contents of the zones, that is aboveabout 900 to 1000 p. s. i. g. Such iiui-dization velocities permitmaintenance of the unagglomerated catalyst partlcles in agitatedsuspension and yet permit the agglomerated particles to settle in themanner heretofore described. By careful control of the uidizationvelocity, agglomeration of catalyst mto large masses may be preventedsince ag anatema zglomerateshavingssizesiotl-onlyisevral tunes-.the

sizesofthellarger.catalystaxparticles will settlebefore'la'rgemasses-may bedormed.

`aivhatislclaimed:is:

'1. In the iprocess of Lfpolymerizingsolefins .to

v`catalyst from.; said. suspension; :washing :it 4.with a:'liquidsolvent k.whereby .itiisldeglomerated and :returninglthe ideglomerated .catalyststo said susnpension, said solventi havingYgood-solvent .propertiesiforssaid-high molecularrweightrhindingmate'rials.V

SZQARprUeeSS inI` vaccordance.withaclaim. .f1 in'. -which osereiLcatalyst -Lcomprisesephosphoric acid 1:- depo'sitedmn assi'liceoiisxcarrienz.

- 23.A processiin accordance withiclaimwherewinJsaid'agglomeratedcatalyst. is mashediwith'z'an rlaromaticihydrocarbon.solvent..v

tained tassa .'-slurnyiainea num-hydrocarbon phase under polymerizationpressure land-temperature :conditions and inrwhichatleastaportionor-said cataylstfcoheres I@intossulzistantially:inactiveagglomerate's'I difcult `to maintain slurrie'd condition, fthe-Iimprovement whichlfcornprises#settling-f and-removingfagglomeratedmatalyst from said slur1 y,' was'shingsaidvagglorneratedvcatalyst withcanra-romatic khydrocarbon *solvent whereby'itris-wzleglornerated-and substantially reactivated, removing isolventL"f-rom- -the-deglomerated catav-lyst,`-and returning fthe=deglomeraterl"catalyst'gto saidslurry.

6. A process in accordance withiclairn''in which Ysaid kpressure ;isabovei about145O1jp.s. -i.,g. `andjsaidrterxnieratnreis inthe range ,oiahl1t`35j0 .7. Agprocess `in 1accordance wit,h.. claim .5 ...in ,whichsaid catalyst ris maintained..in..s1 urried `condition.bY-vpassinaastream; comprisingfhydrocarbonsnpwardly therethrough atasvelocityfsucientatofmaintain'.unagglomerated catalyst z susvxnendedand finsuicientfto :maintain `,sairl agglQmerated..catalyst susp ended.

v8. A process .accordance with claim 7 1in which said hydrocarbon ispassed upwardly :through said ycatalyst at a .velocityin the range Aofabout 1 .tolO feet'per minute.

r9.1. process in accordance with claim rwhereinsaid.agglomeratedcatalyst is withdrawn from said .slurry-,andfis:introduced .into the'top of a 1treating lzone .and Vcountercmrrentlycontacted by nneans of said solvent which is introduced into thezbottomof said treating zone.

110, In the process of polynierizing normally gaseousrolensrto producepolymers boiling in the .gasoline .boilingfrange Vin y.which .a catalystcomprising .phosphoric acid .deposited `on a -siliceous base-.and havingafsize in the range `of about 20 to :200 mesh, is maintained as anagitated suspenvsion :inea hydrocarbon phase, and in which said catalyst:particles agglomerato and Abecome 4suicstantially inactivey afterprolonged contact due tofthe adsorption of-high molecular Weight bodiesthereon, the improvement which comprises settling `agglomerated.catalyst particles from the suspended catalyst, passing theagglomerated catalyst into :a primary .recovery .zone wherein a primaryaromatic hydrocarbon solvent is used .to Wash .said high molecularWeight material i'omsaid catalystto cause deglomeration thereof,Withdravving andfintroducing the catalyst into a secondary recovery.zone wherein it is treated .with a second portion of said primarysolvent, withdrawing the Washedv catalystand introducing itinto atertiary treatingzone .for treatment with a .secondary paranichydrocarbon solvent intorderto remove said primary solvent from saidcatalyst, and. .withdrawing deglomerated catalyst from saidtertiaryzoneand passing same to said .reaction zone.

11.1;Process according-to claim 5 .wherein said agglomerated catalyst iscontinuously withdrawn.. deglomerated land returned.

WALTER G. MAY. .GEORGE L. MATHESON.

:References Cited'in fthe file of this patent UNITED STATES PATENTS

1. IN THE PROCESS OF POLYMERIZING OLEFINS TO PRODUCE LOW BOILING POLYMERS IN WHICH A SOLID, FINELY DIVIDED PHOSPHORIC ACID CATALYST IS MAINTAINED AS AN AGITATED SUSPENSION IN A FLUID HYDROCARBON PHASE COMPRISING SAID OLEFINS AND IN WHICH AT LEAST A PORTION OF SAID CATALYST AGGLOMERATES BY THE BINDING ACTION OF HIGH MOLECULAR WEIGHT MATERIALS ADSORBED THEREON, THE IMPROVEMENT WHICH COMPRISES REMOVING SAID AGGLOMERATED CATALYST FROM SAID SUSPENSION WASHING IT WITH A LIQUID SOLVENT WHEREBY IT IS DEGLOMERATED AND RETURNING THE DEGLOMERATED CATALYST TO SAID SUSPENSION, SAID SOLVENT HAVING GOOD SOLVENT PROPERTIES FOR SAID HIGH MOLECULAR WEIGHT BINDING MATERIALS. 